Pneumatic radial tire for a passenger vehicle and method of using the same

ABSTRACT

A pneumatic radial tire for a passenger vehicle according to the present invention has an appropriate relationship between a tire cross-sectional width SW and a tire outer diameter OD. Also, a method of using the pneumatic radial tire for a passenger vehicle according to the present invention is to use the above radial tire with at least specified internal pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No. 14/240,658, filed Feb. 24, 2014, which is a National Stage of International Application No. PCT/JP2012/005343, filed Aug. 24, 2012, claiming priority based on Japanese Patent Application Nos. 2011-185178, JP 2011-185279 and JP 2011-185195, filed Aug. 26, 2011, the contents of all of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a pneumatic radial tire for a passenger vehicle and a method of using the tire.

BACKGROUND ART

Bias tires having relatively narrower sectional widths had been predominantly used in vehicles until around 1960 because vehicles in those days were relatively lightweight, and the speed demanded for the vehicles were lower, resulting a less burden imposed on the tires. However, radial tires are predominant these days and those having larger widths and assuming flat shapes are particularly demanded due to increase in weight and speed of vehicles (see, for example, PTL 1).

However, the increase in a tire width sacrifices the vehicle space and thus degrades comfortability. This is a major problem particularly for electric vehicles that have been put on practical use in anticipation of future, considering situations where ensuring a space around tires has been becoming of great importance, because the electric vehicles are required to secure a space for accommodating driving components such as a motor for controlling a torque for rotating a tire about a drive shaft.

Further, there has been an increasing demand for lower fuel consumption along with increased interest in environmental issues. Here, it has been known to increase a diameter and a width of the tire in order to reduce a rolling resistance value (RR value) of the tire for better fuel efficiency. However, there is a problem that the increase in the diameter and width of the tire leads to an increase in tire weight and air resistance, which rather increases vehicle resistance and causes excessive tire loading capability.

CITATION LIST Patent Literature

PTL 1: JP H7-40706 A

SUMMARY OF INVENTION Technical Problem

The present invention aims at solving the problems described above and an object thereof is to provide a pneumatic radial tire for a passenger vehicle that is lightweight with less vehicle resistance and thus ensures excellent comfortability, and to provide a method of using the tire.

Solution to Problem

The inventors diligently studied to solve the aforementioned problems.

As a result, the inventors have found that it is extremely effective, for the purpose of improvement in fuel efficiency and comfortability of a radial tire, to appropriately control reduction in a width of the tire and the increase in a diameter, namely, a relationship between a tire cross-sectional width SW and a tire outer diameter OD.

The present invention has been contrived based on the aforementioned knowledge and a summary thereof is as follows:

-   -   (1) A pneumatic radial tire for a passenger vehicle having a         carcass, which is composed of a ply of cords radially arranged         and toroidally provided between a pair of bead cores, and a bead         filler disposed outside the bead cores in a tire radial         direction, wherein

when the radial tire is mounted on a rim and applied with internal pressure of at least 250 kPa,

with a tire cross-sectional width SW of smaller than 165 (mm), a ratio of the tire cross-sectional width SW to a tire outer diameter OD, SW/OD, is no more than 0.26,

with the tire cross-sectional width SW of 165 (mm) or larger, the tire cross-sectional width SW and the tire outer diameter OD satisfy a relational expression:

OD≧2.135'SW+282.3, and

a bead filler tire-width-direction cross-sectional area S1 is one to four times the size of a bead core tire-width-direction cross-sectional area S2.

(2) A pneumatic radial tire for a passenger vehicle having a carcass, which is composed of a ply of cords radially arranged and toroidally provided between a pair of bead cores, and a bead filler disposed outside the bead cores in a tire radial direction, wherein when the radial tire is mounted on a rim and applied with internal pressure of at least 250 kPa, a tire cross-sectional width SW and a tire outer diameter OD satisfy a relational expression:

OD≧−0.0187×SW²+9.15×SW−380, and

a bead filler tire-width-direction cross-sectional area S1 is one to four times the size of a bead core tire-width-direction cross-sectional area S2.

(3) The pneumatic radial tire for a passenger vehicle according to (1) or (2) set forth above, wherein, when BFW represents a width of the bead filler in the tire width direction in a tire radial direction center position of the bead filler and BDW represents a maximum width of the bead core in the tire width direction, the following relational expression:

0.1≦BFW/BDW≦0.5

is satisfied.

(4) The pneumatic radial tire for a passenger vehicle according to any one of (1) to (3) set forth above, wherein, when BFH represents a height of the bead filler in the tire radial direction and SH represents a tire sectional height, the following relational expression:

0.1≦BFH/SH≦0.25

is satisfied.

(5) The pneumatic radial tire for a passenger vehicle according to any one of (1) to (4) set forth above, wherein BFH, the height of the bead filler in the tire radial direction, is no more than 45 mm.

(6) A method of using a pneumatic radial tire for a passenger vehicle, wherein the tire according to (1) or (2) set forth above having the internal pressure of at least 250 kPa is used.

(7) A pneumatic radial tire for a passenger vehicle including a carcass, which is composed of a ply of carcass cords radially arranged and toroidally provided between bead cores embedded in a pair of bead portions, and a pair of sidewall portions connected to the bead portions, wherein

when the tire is mounted on a rim and applied with internal pressure of at least 250 kPa,

with a tire cross-sectional width SW of smaller than 165 (mm), a ratio of the tire cross-sectional width SW to a tire outer diameter OD, SW/OD, is no more than 0.26,

with the tire cross-sectional width SW of 165 (mm) or larger, the tire cross-sectional width SW and the tire outer diameter OD satisfy a relational expression:

OD≧2.135×SW+282.3, and

a ratio Ts/Tb is 15% to 40%, the Ts representing a gauge of the sidewall portion in a maximum width portion of the tire and the Tb representing a bead width of the bead core in a tire radial direction center position.

(8) A pneumatic radial tire for a passenger vehicle including a carcass, which is composed of a ply of carcass cords radially arranged and toroidally provided between bead cores embedded in a pair of bead portions, and a pair of sidewall portions connected to the bead portions, wherein

when the tire is mounted on a rim and applied with internal pressure of at least 250 kPa, a tire cross-sectional width SW and a tire outer diameter OD satisfy a relational expression:

OD≧−0.0187×SW²+9.15×SW−380, and

a ratio Ts/Tb is 15% to 40%, the Ts representing a gauge of the sidewall portion in a tire maximum width portion and the Tb representing a bead width of the bead core in a tire radial direction center position.

(9) The pneumatic radial tire for a passenger vehicle according to (7) or (8) set forth above, wherein the gauge Ts of the sidewall portion in the tire maximum width portion is no less than 1.5 mm.

(10) The pneumatic radial tire for a passenger vehicle according to any one of (7) to (9) set forth above, wherein a diameter Tbc of the bead core is 4 mm to 12 mm.

(11) A method of using a pneumatic radial tire for a passenger vehicle, wherein the tire according to (7) or (8) set forth above having internal pressure of at least 250 kPa is used.

(12) A pneumatic radial tire for a passenger vehicle including a carcass, which is composed of a ply of carcass cords radially arranged and toroidally provided between a pair of bead portions, and a pair of sidewall portions connected to the bead portions, wherein

when the tire is mounted on a rim and applied with internal pressure of at least 250 kPa,

with a tire cross-sectional width SW of smaller than 165 (mm), a ratio of the tire cross-sectional width SW to a tire outer diameter OD, SW/OD, is no more than 0.26,

with the tire cross-sectional width SW of 165 (mm) or larger, the tire cross-sectional width SW and the tire outer diameter OD satisfy a relational expression:

OD≧2.135×SW+282.3, and

a ratio Ts/Tc is 5 to 10, the Ts representing a gauge of the sidewall portion in a tire maximum width portion and Tc representing a diameter of the carcass cord.

(13) A pneumatic radial tire for a passenger vehicle including a carcass, which is composed of a ply of carcass cords radially arranged and toroidally provided between a pair of bead portions, and a pair of sidewall portions connected to the bead portions, wherein

when the tire is mounted on a rim and applied with internal pressure of at least 250 kPa, a tire cross-sectional width SW and a tire outer diameter OD satisfy a relational expression:

OD≧−0.0187×SW²+9.15×SW−380, and

a ratio Ts/Tc is 5 to 10, the Ts representing a gauge of the sidewall portion in a tire maximum width portion and Tc representing a diameter of the carcass cord.

(14) The pneumatic radial tire for a passenger vehicle according to (12) or (13) set forth above, wherein, when Ta represents a distance in a tire width direction from a surface of the carcass cord to a tire outer surface, a ratio Ta/Tc is 3 to 6.

(15) The pneumatic radial tire for a passenger vehicle according to any one of (12) to (14) set forth above, wherein the diameter Tc of the carcass cord is 0.4 mm to 0.8 mm.

(16) A method of using a pneumatic radial tire for a passenger vehicle, wherein the tire according to (12) or (13) set forth above having internal pressure of at least 250 kPa is used.

Advantageous Effect of Invention

According to the present invention, a pneumatic radial tire for a passenger vehicle that is lightweight having less vehicle resistance and thus capable of providing excellent comfortability may be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) is a side view of a tire, and FIG. 1(b) is a cross-sectional view in a tire circumferential direction illustrating the proximity of a ground-contact surface of the tire;

FIG. 2 is a graph illustrating a relationship between a tire outer diameter OD and a tire deflection amount δ1;

FIGS. 3(a), (b) are diagrams illustrating tire deformations;

FIGS. 4(a), (b) are cross-sectional diagrams in a tire width direction illustrating tire deformations;

FIG. 5 is a graph illustrating a relationship between a ground-contact width W and a deflection amount δ2;

FIG. 6 is a diagram illustrating a relationship among a load, internal pressure, and a ground-contact area;

FIG. 7(a) is a graph illustrating the deflection amount δ1 of the tire having high internal pressure, and FIG. 7(b) is a graph illustrating the ground-contact area when the tire is applied with high internal pressure;

FIGS. 8(a), (b) are diagrams illustrating vehicle space ensured by the tire with a larger diameter and a narrower width;

FIG. 9 is a graph illustrating a relationship between the tire internal pressure and a tire rolling resistance value (RR value);

FIGS. 10(a), (b) are graphs illustrating weight and the rolling resistance value of each tire;

FIGS. 11(a), (b) are graphs illustrating a ground-contact length and the rolling resistance value of each tire;

FIGS. 12(a), (b) are graphs illustrating the deflection amount δ1 and the ground-contact length of each tire;

FIG. 13 is a graph illustrating a relationship between a ground-contact width and the rolling resistance value of each tire;

FIGS. 14(a), (b) are graphs illustrating a relationship between SW and OD of test tires and conventional tires;

FIG. 15 is a graph illustrating the weight and the rolling resistance value of each tire;

FIG. 16 is a cross-sectional view in a tire width direction of a pneumatic radial tire for a passenger vehicle according to the present invention;

FIG. 17 is a cross-sectional view in a tire width direction of a pneumatic radial tire for a passenger vehicle according to the present invention;

FIG. 18(a) is a schematic diagram illustrating a size of a member around sidewall portion, and FIG. 18(b) is a schematic diagram illustrating a size of a member around the bead portion;

FIG. 19 is a cross-sectional diagram in the tire width direction of the pneumatic radial tire for a passenger vehicle according to the present invention;

FIG. 20 is a schematic diagram illustrating a size of a tire member around the sidewall portion;

FIGS. 21(a), (b) are graphs illustrating results of an evaluation of a tire performance test;

FIGS. 22(a), (b) are graphs illustrating results of an evaluation of a tire performance test;

FIGS. 23(a), (b) are graphs illustrating results of an evaluation of a tire performance test;

FIGS. 24(a), (b) are graphs illustrating results of an evaluation of a tire performance test;

FIGS. 25(a), (b) are graphs illustrating results of an evaluation of a tire performance test; and

FIGS. 26(a), (b) are graphs illustrating results of an evaluation of a tire performance test.

DESCRIPTION OF EMBODIMENTS

The following is a description of a process that led to a pneumatic radial tire for a passenger car (hereinafter, referred to as a tire) according to the present invention.

FIG. 1(a) illustrates a tire crown portion bending upon application of a load. Due to the bending of the crown portion, as schematically illustrated in a parallelogram in FIG. 1(a), tread rubber undergoes shear deformation in a tire circumferential direction, which repeatedly occurs during rotation of the tire, causing energy loss and the increase in tire rolling resistance.

As such, in order to reduce a rolling resistance value, first, reduction in a deflection amount of the tire during ground contact becomes of importance.

FIG. 1(b) is a cross-sectional view in a circumferential direction of the tire in the proximity of a ground-contact surface thereof. As illustrated in FIG. 1(b), when OD (mm), δ1 (mm), and L (mm) represent a tire outer diameter, a deflection amount, and a ground-contact length in the circumferential direction, respectively, the deflection amount δ1 may be approximately represented by, in a geometrical manner, the following two formulae:

δ1=(OD/2)×(1−cos θ)  (Formula 1)

θ≈ tan⁻¹{(L/2)/(OD/2)}≈L/OD  (Formula 2)

Also, FIG. 2 is a graph illustrating a relationship between the tire outer diameter OD and the deflection amount δ1 when conventional tires in various sizes are mounted on an application rim and applied with prescribed internal pressure and a maximum load.

Here, the “application rim” for the conventional tire is defined by industrial standards valid in areas where the tire is produced and used, such as JATMA (Japan Automobile Tire Manufacturers Association) YEAR BOOK in Japan, ETRTO (European Tyre and Rim Technical Organization) STANDARD

MANUAL in Europe, and TRA (THE TIRE and RIM ASSOCIATION INC.) YEAR BOOK in the United States. Also, the “prescribed internal pressure” is based on a correspondence table of the application rim corresponding to a size of a radial ply tire as defined in the above-mentioned JATMAYEAR BOOK (Japan Automobile Tire Manufacturers Association Standards) and the like, the air pressure, and a load capacity. Further, the term “maximum load” means a maximum load (maximum load capacity) of a single tire in an appropriate size prescribed in the above-mentioned predetermined industrial standards.

From Formulae 1 and 2 set forth above and FIG. 2, it can be seen that, in order to reduce the deflection amount δ1, it is effective to increase the tire outer diameter OD.

That is, in order to reduce the tire rolling resistance from a viewpoint of suppression of the shear deformation of tread rubber in the tire circumferential direction, it is effective to increase a tire diameter.

Further, from the following Formula representing a tire belt tension, it can be seen that the tire belt tension increases along with the increase in the tire diameter.

T=(OD/2)×P  (Formula 3)

Along with the increase in the tire belt tension, tire ring rigidity (rigidity for keeping a ring shape of the tire) also increases, which, as illustrated in FIGS. 3(a), (b), promotes deformation eccentrically moving the entire ring (i.e., eccentric deformation) while the tire is maintained in the ring shape. Thereby, deformation of the tread rubber is suppressed, reducing the tire rolling resistance value.

That is, the increase in the tire diameter is effective in reducing the tire rolling resistance value, also from a viewpoint of suppressing deformation of the ring shape of the tire.

Next, the inventors focused on the shear deformation of the tread rubber in the tire width direction.

That is, deflection of the crown portion when the tire contacts the ground, as schematically illustrated by a parallelogram of FIG. 4(a), causes shear deformation of the tread rubber in the tire width direction, which repeatedly occurs during rotation of the tire, causing energy loss and the increase in the rolling resistance.

FIG. 4(b) is a cross-sectional view of a tire ground-contact surface in the tire width direction. As illustrated in FIG. 4(b), in the cross-section in the tire width direction, each of points E1 and E2 represents a contact end upon application of a maximum load defined for each vehicle wearing the tire, a point F represents a width direction center position, and W (mm) represents a width direction contact width.

Also, in a no-load state, CR (mm) represents a crown radius at each of the points E1 and E2 on a curve including the three points E1, E2, and F approximated by a circular arc in the width-direction cross-section, and O represents a center of a circle made on the basis of the circular arc. Here, in the width-direction cross-section, a line segment OE1 forms an angle γ(°) with respect to a tire equator plane.

Further, when a deflection amount δ2 (mm) (an amount of deflection of ground-contact ends in the width direction) represents a deflection amount upon application of a maximum load defined for each vehicle wearing the tires described above, the δ2 may be approximately expressed by the following formulae in a geometrical manner:

δ2=CR×(1−cos γ)  (Formula 4)

γ≈ tan⁻¹{(W/2)/CR}≈W/2CR  (Formula 5)

Also, FIG. 5 is a graph illustrating a relationship between the contact width W and the deflection amount δ2 when conventional tires in various sizes are mounted on the application rim and applied with the prescribed internal pressure and the maximum load.

As can be seen from Formulae 4, 5 set forth above and FIG. 5, reduction in the ground-contact width W may reduce the deflection amount δ2. That is, in order to reduce the tire rolling resistance from a viewpoint of suppression of the shear deformation of the tread rubber in the tire width direction, it is effective to reduce a tire width.

The reduction in the tire width is also effective to reduce tire weight.

As described above, it has been found that appropriate regulation of the increase in the tire diameter and the reduction in the tire width enables reduction in the tire rolling resistance value while reducing the tire weight.

As illustrated in FIG. 6, incidentally, when L, W, P, and Lo represent the ground-contact length, the ground-contact width, the internal pressure, and a load on the tire, respectively, a relationship between a ground-contact area of the tire and the applied load satisfies the following relational expression:

Lo≈W×L×P,  (Formula 6)

which is derived from an equilibrium-force condition.

Therefore, under a condition with a certain load applied on the tire and certain internal pressure, when the ground-contact width W of the tire is reduced so as to suppress the shear deformation of the tread rubber in the width direction and also to reduce the tire weight as described above, the ground-contact length L increases, as can be seen from the relational expression of a balance of Formula 6 set forth above.

Accordingly, it has been newly found that, according to Formulae 1, 2 set forth above, the increase in the deflection amount δ1 due to the increase in the ground-contact length L leads to the increase in the shear deformation of the tread rubber in the tire circumferential direction.

As such, the inventors have found that, as a method to suppress the increase in the ground-contact length while reducing the width of the tire, it is effective to use the tire with high internal pressure.

That is, based on the relational expression of Formula 6 set forth above, regardless of the reduction in the ground-contact width, the tire with high internal pressure may support an applied load without reducing the ground-contact length.

FIG. 7(a) is a graph illustrating a relationship between the ground-contact width W and the deflection amount δ1 of a tire of 195/65R15 in size mounted on the application rim and applied with the maximum load. FIG. 7(b) is a graph illustrating a relationship between the ground-contact width W and the ground-contact area of the tire of 195/65R15 in size mounted on the application rim and applied with the maximum load.

As illustrated in FIG. 7(a), when the tire with prescribed internal pressure is used, the ground-contact width reduces and thus the deflection amount δ1 increases, reducing the effect to reduce the shear deformation of the tread rubber in the circumferential direction. As illustrated in FIG. 7(b), also, the ground-contact area remains approximately the same regardless of the reduction in the ground-contact width while the ground-contact length increases.

On the other hand, by using the tire with high internal pressure, the increase in the deflection amount may be suppressed regardless of the reduction in the ground-contact width as illustrated in FIG. 7(a) and, by reducing the ground-contact width, the ground-contact area may also be reduced as illustrated in FIG. 7(b).

Accordingly, the shear deformation of the tread rubber in the circumferential direction when the tire contacts the ground may be suppressed, thus reducing the tire rolling resistance value.

Further, as illustrated in FIGS. 8(a), (b), the reduction in the tire width may ensure a space inside/outside a vehicle; in particular, a space for accommodating driving components in the proximity of an inner side of the tire. Also, the increase in the diameter of the radial tire increases a height of a drive shaft and an under-chassis space, securing spaces for a car trunk and the like and also a space for accommodating driving units.

On the basis of the findings described above, the inventors investigated for specific conditions under which the increase in the tire diameter, the reduction in the tire width, and application of high internal pressure may achieve both the reduction in the tire rolling resistance value and the tire weight.

First, as a referential tire for evaluation, a tire of 195/65R15 in size was prepared, because such a tire has been used for the most common types of vehicles and thus suitable for comparison of tire performance.

Tires in various sizes were also prepared, which were mounted on a rim with a width corresponding to a bead width of the tire and applied with the internal pressure of 220 kPa, or applied with high internal pressure. Then, tests were conducted as described below.

Table 1 shows specifications of each of the tires. Other specifications such as internal structures of the tires that are not shown in Table 1 are similar to those of common tires. Each of the tires includes a carcass composed of a ply of cords radially arranged and toroidally provided between a pair of bead portions.

With regard to the tire size, the inventors studied using tires in various sizes including conventional sizes prescribed in JATMA (the tire standard in Japan), TRA (the tire standard in the United States), ETRTO (the tire standard in EU) and the like, as well as using tires in non-standard sizes.

Especially assuming a sporty application, test tires 27 to 33 with a tire cross-sectional width SW of at least 175 (mm) were also prepared.

Here, the test tires 27 to 33 were compared with a tire of 225/45R17 in size (Reference Tire 2), which is larger than the tire of 195/65R15 in size (Reference Tire 1) by an inch.

TABLE 1 Ratio Tire Size SW/OD Conventional Conventional 145/70R12 0.29 Tire Tire 1 Conventional 155/55R14 0.29 Tire 2 Conventional 165/60R14 0.30 Tire 3 Conventional 175/65R14 0.30 Tire 4 Conventional 185/60R15 0.31 Tire 5 Reference Tire 1 195/65R15 0.31 Conventional 205/55R16 0.32 Tire 6 Conventional 215/60R16 0.32 Tire 7 Conventional 225/55R17 0.33 Tire 8 Conventional 245/45R18 0.36 Tire 9 Conventional 155/65R13 0.29 Tire 10 Reference Tire 2 225/45R17 0.35 Test tire Test tire 1 165/65R19 0.24 Test tire 2 155/65R18 0.24 Test tire 3 145/65R19 0.22 Test tire 4 135/65R19 0.21 Test tire 5 125/65R19 0.19 Test tire 6 175/55R22 0.23 Test tire 7 165/55R20 0.24 Test tire 8 155/55R19 0.24 Test tire 9 145/55R20 0.22 Test tire 10 135/55R20 0.21 Test tire 11 125/55R20 0.19 Test tire 12 175/45R23 0.24 Test tire 13 165/45R22 0.23 Test tire 14 155/45R21 0.23 Test tire 15 145/45R21 0.22 Test tire 16 135/45R21 0.21 Test tire 17 145/60R16 0.25 Test tire 18 155/60R17 0.25 Test tire 19 165/55R19 0.25 Test tire 20 155/45R18 0.26 Test tire 21 165/55R18 0.26 Test tire 22 175/55R19 0.26 Test tire 23 115/50R17 0.21 Test tire 24 105/50R16 0.21 Test tire 25 135/60R17 0.23 Test tire 26 185/60R20 0.25 Test tire 27 185/50R20 0.27 Test tire 28 195/60R19 0.27 Test tire 29 175/60R18 0.26 Test tire 30 195/55R20 0.27 Test tire 31 215/50R21 0.29 Test tire 32 205/55R20 0.28 Test tire 33 185/45R22 0.26

<Rolling Resistance Value (RR Value)>

Each of the tires set forth above was mounted on the rim with the width corresponding to the bead width of the tire to obtain a tire-rim assembly. The tire was then applied with the maximum load prescribed for each vehicle wearing the tire and run at a drum rotation speed of 100 km/h, for measurement of the rolling resistance.

Results of an evaluation are shown as indices relative to that of Reference Tire 1 set to 100. The smaller the index, the smaller the rolling resistance.

<Tire Weight>

Weight of each of the tire was measured and is shown as index relative to that of Reference Tire 1 set to 100 (the smaller the index, the lighter the weight).

Results of an evaluation are shown in Tables 2 and 3 below, based on which the results are further illustrated in FIGS. 10 to 13.

TABLE 2 RR Internal Tire Value Pressure W L OD δ1 Weight 220 kPa (INDEX) (kPa) (mm) (mm) (mm) (mm) (INDEX) Conventional Conventional 120 220 111.65 162.8 507.8 12.1 61.3 Tire Tire 1 Conventional 125 220 119.35 152.3 526.1 10.4 61.9 Tire 2 Conventional 118 220 127.05 143.1 553.6 8.8 71.6 Tire 3 Conventional 109 220 134.75 134.9 583.1 7.5 82.5 Tire 4 Conventional 106 220 142.45 127.6 603 6.5 87.4 Tire 5 Reference 100 220 150.15 121.1 634.5 5.6 100 Tire 1 Conventional 101 220 157.85 115.2 631.9 5.1 98.3 Tire 6 Conventional 93 220 164.65 110.4 664.4 4.5 111.9 Tire 7 Conventional 85 220 170.85 106.4 679.3 4.1 124.7 Tire 8 Conventional 80 220 176.65 102.9 677.7 3.8 129.4 Tire 9 Conventional 90 220 170.8 106.4 634.3 4.4 116.5 Tire 10 Reference 90 220 170.8 106.5 634.3 4.37 116 Tire 2 Test Tire Test Tire 1 98.9 220 127.1 143.1 697.1 7.1 93 Test Tire 2 106.7 220 119.4 152.3 658.7 8.5 82.5 Test Tire 3 107.5 220 111.7 162.8 671.1 9.5 78.6 Test Tire 4 111.7 220 104 174.9 658.1 11 71.8 Test Tire 5 116 220 96.3 188.9 645.1 13 65.2 Test Tire 6 88.3 220 134.8 134.9 751.3 5.9 99.7 Test Tire 7 99.3 220 128.3 141.7 689.5 7.1 86.3 Test Tire 8 106.8 220 120.5 150.8 653.1 8.4 76.8 Test Tire 9 107.4 220 112.8 161.2 667.5 9.3 73.4 Test Tire 10 111.4 220 105 173.2 656.5 10.9 67.2 Test Tire 11 115.4 220 97.2 187 645.5 12.8 61.2 Test Tire 12 89 220 136.1 133.6 741.7 5.9 92 Test Tire 13 96.3 220 129.6 140.3 707.3 6.8 82.7 Test Tire 14 103.5 220 121.7 149.3 672.9 8 73.9 Test Tire 15 107.2 220 113.9 159.6 663.9 9.2 68.2 Test Tire 16 111 220 106 171.5 654.9 10.7 62.7 Test Tire 17 102.7 220 114.6 158.7 580.4 10.2 65.9 Test Tire 18 100.1 220 122.5 148.4 617.8 8.5 75 Test Tire 19 94.2 220 130.4 139.4 664.1 7 83.1 Test Tire 20 105 220 122.5 148.4 596.7 8.8 65.5 Test Tire 21 96.2 220 130.4 139.4 638.7 7.3 79.9 Test Tire 22 93.6 220 131.3 138.5 675.1 6.2 89.6 Test Tire 23 118 220 92.0 197.6 546.8 16.3 48.2 Test Tire 24 120 220 89.3 203.7 511.4 18.2 41.2 Test Tire 25 113 220 108.0 168.3 593.8 11.3 65.9 Test Tire 26 102 220 138.8 131.0 730 5.7 109.4 Test Tire 27 89.2 220 138.8 131.0 693.0 6.0 104.7 Test Tire 28 90.9 220 146.3 124.3 716.6 5.3 109.5 Test Tire 29 92.9 220 131.3 138.5 667.2 7.0 102.4 Test Tire 30 95.8 220 136.5 133.2 722.5 6.0 106.9 Test Tire 31 81.9 220 150.5 120.8 748.4 4.8 114.1 Test Tire 32 85.4 220 143.5 126.7 733.5 5.4 112.0 Test Tire 33 91.4 220 131.3 138.5 716.3 6.5 102.0

TABLE 3 RR Internal Tire High Internal Value Pressure W L OD δ1 Weight Pressure (INDEX) (kPa) (mm) (mm) (mm) (mm) (INDEX) Conventional Conventional 108 295 111.7 121.4 507.8 7 61.3 Tire Tire 1 Conventional 111.3 275 119.4 121.9 526.1 6.8 61.9 Tire 2 Conventional 108.6 260 127.1 121.1 553.6 6.4 71.6 Tire 3 Conventional 103.6 245 134.8 121.2 583.1 6.1 82.5 Tire 4 Conventional 103.9 230 142.5 122.1 603 6 87.4 Tire 5 Reference 100 220 150.2 121.1 634.5 5.6 100 Tire 1 Conventional 101 220 157.9 115.2 631.9 5.1 98.3 Tire 6 Conventional 93 220 164.7 110.4 664.4 4.5 111.9 Tire 7 Conventional 85 220 170.9 106.4 679.3 4.1 115.9 Tire 8 Conventional 80 220 176.7 102.9 677.7 3.8 117.7 Tire 9 Conventional 90 220 170.8 106.4 634.3 4.4 116.5 Tire 10 Reference 90 220 170.8 106.5 634.3 4.37 116 Tire 2 Test Tire Test Tire 1 92.2 260 127.1 121.1 697.1 5.1 93 Test Tire 2 96 275 119.4 120.6 658.7 5.4 82.5 Test Tire 3 92.4 295 111.7 121.4 671.1 5.4 78.6 Test Tire 4 91.6 315 104 121 658.1 5.4 71.8 Test Tire 5 88.2 340 96.3 121.2 645.1 5.5 65.2 Test Tire 6 84.8 345 134.8 120.7 751.3 4.8 99.7 Test Tire 7 92.6 260 128.3 120.8 689.5 5.2 86.3 Test Tire 8 96.2 275 120.5 121.1 653.1 5.5 76.8 Test Tire 9 92.3 290 112.8 121.1 667.5 5.4 73.4 Test Tire 10 92.4 310 105 121.7 656.5 5.5 67.2 Test Tire 11 87.7 340 97.2 121 645.5 5.5 61.2 Test Tire 12 85.5 250 136.1 120.9 741.7 4.8 92 Test Tire 13 89.7 255 129.6 121 707.3 5.1 82.7 Test Tire 14 93.2 270 121.7 121.2 672.9 5.3 73.9 Test Tire 15 92.2 290 113.9 121.1 663.9 5.4 68.2 Test Tire 16 92.1 310 106 121.3 654.9 5.5 62.7 Test Tire 17 93.9 290 114.6 120.4 580.4 6 65.9 Test Tire 18 92.1 270 122.5 120.9 617.8 5.7 75 Test Tire 19 89.4 255 130.4 120.3 664.1 5.3 83.1 Test Tire 20 92.1 270 122.5 120.9 596.7 5.9 65.5 Test Tire 21 89.4 255 130.4 120.3 638.7 5.5 79.9 Test Tire 22 88.7 250 131.3 121.9 675.1 5.3 89.6 Test Tire 23 86.7 350 92.0 124.2 546.8 6.8 48.2 Test Tire 24 94.1 350 89.3 128.0 511.4 7.66 41.2 Test Tire 25 85.6 300 108.0 123.4 593.8 6.22 65.9 Test Tire 26 73.0 270 138.8 106.7 730 3.84 109.4 Test Tire 27 80.0 270 104.7 106.8 693.0 4.0 104.7 Test Tire 28 81.3 258 109.5 106.0 716.6 3.9 109.5 Test Tire 29 84.7 286 102.4 106.6 667.2 4.2 102.4 Test Tire 30 83.3 277 106.9 105.8 722.5 3.8 106.9 Test Tire 31 75.0 250 114.1 106.3 748.4 3.7 114.1 Test Tire 32 78.7 263 112.0 106.0 733.5 3.8 112.0 Test Tire 33 86.7 285 100.0 106.9 716.3 3.9 102.0

Also, by using the test tires 8, 15, 20, and 31 with various internal pressure, the tests for evaluation of the tire rolling resistance value were conducted in the method described above.

Results of the an evaluation are shown in Table 4 and FIG. 9.

TABLE 4 Internal Tire Size Pressure 145/45R21 155/55R19 155/45R18 215/50R21 (kPa) RR Value (INDEX) 220 106.8 107.2 105 102 250 99 99 97 95 280 96 93 91 88 310 91.8 88.5 87 84 340 88 85 84 81 400 83 79 79 77

From Tables 2 to 4 and FIGS. 9, 10(a), (b), it can be seen that, when the test tires 1 to 26 with the internal pressure of at least 250 kPa are used, both the tire rolling resistance value and the tire weight may be reduced comparing to those of Reference Tire 1. It can also be seen that, when the test tires 27 to 33 with the internal pressure of at least 250 kPa are used, both the tire rolling resistance value and the tire weight may be reduced comparing to those of Reference Tire 2.

Note that the internal pressure is preferably no more than 350 kPa.

Here, the inventors have studied in more detail about sizes of the test tires 1 to 33 that allow reduction in both the tire rolling resistance value and the tire weight.

FIGS. 14(a), (b) are graphs illustrating a relationship of a cross-sectional width SW (mm) and an outer diameter OD (mm) of the test tires and the conventional tires.

As illustrated in FIG. 14(a), when the cross-sectional width SW is 165 (mm) or smaller, a ratio SW/OD of the test tires are no more than 0.26. That is, it can be seen that, when the internal pressure is set to 250 kPa or more, tires with the ratio SW/OD of no more than 0.26 may reduce both the tire rolling resistance and the tire weight.

As illustrated in FIG. 14(a), also, when the cross-sectional width SW is 165 (mm) or greater, the cross-sectional width SW and the outer diameter OD of the test tire satisfy the following relational expression:

OD≧2.135×SW+282.3

That is, when the cross-sectional width SW is 165 (mm) or greater, the tires with the internal pressure of 250 kPa or more that satisfy the above relational expression may reduce both the tire rolling resistance value and the tire weight.

As illustrated in FIG. 14 (b), further, as a result of fitting using a quadratic curve boundary of a tire size that enables reduction in both the tire rolling resistance value and the tire weight in conjunction with the tire with SW of smaller than 165 (mm) and the tire with SW of 165 (mm) or greater, it was found that a tire that satisfies the following relational expression:

OD≧0.0187×SW²+9.15×SW−380

may reduce both the tire rolling resistance value and the tire weight.

In order to reduce both the tire rolling resistance value and the tire weight together, SW/OD≦0.26 is preferably satisfied, and SW/OD≦0.24 is particularly preferably satisfied.

Also, from Tables 2, 3 and FIGS. 11(a), (b), it can be seen that applying high internal pressure may suppress the increase in the ground-contact length caused by the reduction in the ground-contact width, such that the ground-contact length becomes similar to that of Reference Tires.

As can be seen in Table 2 and FIG. 12(a), further, when the internal pressure is at 220 kPa, reducing the ground-contact width increases the ground-contact length and the deflection amount δ1. As can be seen in Table 2 and FIG. 12 (b), on the other hand, applying high internal pressure suppresses the increase in the ground-contact length, reducing the deflection amount δ1.

As can be seen in Table 3 and FIG. 13, accordingly, when a tire, which is in size with the tire cross-sectional width SW and the outer diameter OD satisfying SW/OD≦0.26 (SW<165 (mm)) mounted on a rim with a width corresponding to the bead width of the tire and applied with the maximum load defined for each vehicle wearing the tire, is used to have the ground-contact width of no more than 150 mm, the reduction in both the tire rolling resistance value and the tire weight may be achieved. It can also be seen that, when a tire, which is in size satisfying OD≧2.135×SW+282.3 (SW≧165 (mm)) mounted on the rim with the width corresponding to the bead width of the tire and applied with the maximum load defined for each vehicle wearing the tire, is used to have the ground-contact width of no more than 175 mm, the reduction in both the tire rolling resistance value and the tire weight may be achieved.

Alternatively, when a tire, which is in size satisfying OD≧−0.0187×SW²+9.15×SW−380 mounted on the rim with the width corresponding to the bead width of the tire and applied with the maximum load defined for each vehicle wearing the tire, is used to have the ground-contact width of no more than 175 mm, the reduction in both the tire rolling resistance value and the tire weight may be achieved. Note that, in FIG. 13, INDEX 100 means a tire with the ground-contact width of 150 mm. The smaller the number, the smaller the ground-contact width.

The ground-contact width, from a viewpoint of enhancing the safety and stability of the vehicle by securing a tire axial force, is preferably no less than 90 mm.

At this time, the ground-contact length is preferably 90 to 140 mm.

Upon application of a maximum load defined for each vehicle wearing a tire in size with the tire cross-sectional width SW and the outer diameter OD satisfying SW/OD≦0.26 (SW<165 (mm)) and, simultaneously, OD≧2.135×SW+282.3 when taking a linear expression boundary, or OD≧−0.0187×SW²+9.15×SW−380 when taking a quadratic boundary, a ground-contact area of the tire is preferably no more than 16000 mm². Thereby, reduction in both the tire rolling resistance and the tire weight may be achieved.

Note that, from the viewpoint of enhancing the safety and stability of the vehicle by securing the tire axial force, the ground-contact area is preferably no less than 10000 mm².

In order to see an effect of the high internal pressure, tires in further various sizes applied with different internal pressure were used for evaluation of the tire rolling resistance and the tire weight.

Specifications of each of the tires and results of the evaluation are shown in Table 5 and FIG. 15.

TABLE 5 Internal RR Tire Pressure Value Weight Tire Size (kPa) (Index) (Index) Conventional 145/70R12 220 120 45 Tire 155/55R14 220 125 49 165/60R14 220 118 61 175/65R14 220 109 74 185/60R15 220 106 83 195/65R15 220 100 100 205/55R16 220 101 101 215/55R17 220 93 121 225/55R17 220 85 131 245/45R18 220 80 136 225/45R17 220 90 116.5 Internal 145/70R19 265 92.5 79 Pressure 155/55R20 256 93.8 75 Similar to 165/60R20 250 95.1 93 Deflection 175/60R19 250 93.2 92 Amount δ1 High Internal 145/70R19 270 90.7 79 Pressure 155/55R20 270 88.9 75 (Case 1) 165/60R20 270 87 93 175/60R19 270 85.5 92 High Internal 145/70R19 320 76.6 79 Pressure 155/55R20 320 75 75 (Case 2) 165/60R20 320 73.4 93 175/60R19 320 72.9 92

As shown in Table 5 and FIG. 15, by using a tire, which is in size satisfying, under a condition with high internal pressure that allows the 61 to be similar regardless of the reduction in the ground-contact width, SW/OD≦0.26 (SW<165 (mm)) and, simultaneously, OD≧2.135×SW+282.3 (SW≧162 (mm)) (it may also be referred to as a relational expression A) when taking the linear expression boundary, or OD≧−0.0187×SW²+9.15×SW−380 (it may also be referred to as a relational expression B) when taking the quadratic boundary, both the tire rolling resistance and the tire weight may be reduced.

It can also be seen that, by using the tire in size satisfying the relational expression A or the relational expression B described above applied with the internal pressure of no less than 270 kPa, the tire rolling resistance may be significantly reduced and, with the internal pressure of no less than 320 kPa, the tire rolling resistance may be even further reduced.

Here, a preferable tire structure for use with high internal pressure of no less than 250 kPa will be described.

First, the carcass preferably has at least one carcass ply having an end in a high turn-up structure positioning outside a tire maximum width portion in a tire radial direction. More preferably, the end portion has what is called an envelope structure positioning between the carcass and a belt in the tire radial direction.

As for the belt, one with high rigidity is preferably used. More specifically, a belt cord with Young's modulus of 45000 MPa or higher is preferably used.

Thereby, the carcass structure and the rigidity of the belt are optimized, ensuring a tire durable with high internal pressure.

Further, an inner liner of the tire preferably has a thickness of no less than 0.6 mm, so as to prevent air leak under a high internal pressure condition.

Here, the inventors have also found these problems specific to a tire with a small width, a large diameter and high internal pressure that the tire with a smaller width as described above has a smaller deflection amount on the ground-contact area, that a belt tension is increased due to the large radial and high internal pressure which increases a vertical spring coefficient, and that the comfortability is degraded. As such, the inventors have diligently studied to solve those problems and acquired a knowledge of a tire structure that may solve the problems.

The following is a description of a structure of a pneumatic radial tire with a small width, a large diameter and high internal pressure for a passenger vehicle that improves the comfortability.

FIG. 16 is cross-sectional view of a tire in the tire width direction according to a first embodiment of the present invention.

FIG. 16 illustrates a half portion of the tire in the tire width direction from a tire equatorial plane CL serving as a boundary.

Note that this tire is in size satisfying the relational expression A or the relational expression B.

As illustrated in FIG. 16, the tire according to the present embodiment includes a belt 3, which is made up of two belt layers 3 a, 3 b by way of example in the figure at a position radially outside the carcass 2 that is composed of a ply of carcass cords radially arranged and toroidally provided around the bead core 1 a embedded in a pair of bead portions 1 of the tire, and a bead filler 4 disposed at a position radially outside the bead core 1 a.

Here, the bead filler 4 is a high-rigidity member having 100% modulus at room temperature at, for example, 24 to 31 (MPa) in conformity to JIS K6251 (revised on Dec. 20, 2010).

Here, in the tire of the present embodiment, a tire-width-direction cross-sectional area S1 of the bead filler 4 is 1 to 4 times the size of a tire-width-direction cross-sectional area S2 of the bead core 1 a.

Note that, when the tire has a holding bead core structure in which the carcass is held from both inner side and outer side in the tire width direction, a total volume of the bead core inside and outside the carcass in the tire width direction is defined as S2.

The following is a description of an operation and an effect of the present embodiment.

The cross-section of the bead filler 4 within an above-mentioned range enables reduction in the volume of the bead filler, which is the high-rigidity member, and also in the vertical spring coefficient of the tire, thereby improving the comfortability. The tire weight may be reduced also by reducing weight of the bead filler, whereby the tire rolling resistance may be further reduced.

Especially, since the tire with a small width and a large diameter satisfying the relational expression A or the relational expression B has high tension rigidity of the belt and low tension rigidity in the tire side portion compared to that of the belt, limiting the cross-sectional area S1 of the bead filler within the predetermined range as described above is highly effective in reduction of the vertical spring coefficient.

Here, when the tire-width-direction cross-sectional area S1 of the bead filler 4 is larger than 4 times the size of the tire-width-direction cross-sectional area S2 of the bead core 1, the volume of the bead filler made of the high-rigidity member increases, suppressing sufficient reduction in the vertical spring coefficient of the tire and degrading the comfortability.

On the other hand, when the tire-width-direction cross-sectional area S1 of the bead filler 4 is smaller than the tire-width-direction cross-sectional area S2 of the bead core 1 a, the rigidity of the bead portion is significantly reduced and a lateral spring coefficient becomes too small to ensure steering stability.

According to the present embodiment, also, as illustrated in FIG. 16, when BFW represents a width of the bead filler 4 in the tire width direction in a tire radial direction center position and BDW represents a maximum width of the bead core 1 a in the tire width direction,

0.1≦BFW/BDW≦0.5

is preferably satisfied.

This is because, when the ratio BFW/BDW is no more than 0.5, the volume of the bead filler may be reduced while a height thereof is maintained, which enables the reduction in the vertical spring coefficient while maintaining the rigidity in the tire rotational direction. Accordingly, the comfortability may be improved and the tire weight may be reduced.

Also, when the ratio BFW/BDW is no less than 1.0, the rigidity of the bead portion may be ensured and the vertical spring coefficient may be maintained, thereby further ensuring the steering stability.

According to the present embodiment, further, as illustrated in FIG. 16, when BFH represents a height of the bead filler 4 in the tire radial direction and SH represents a sectional height of the tire (tire cross-sectional height),

0.1≦BFH/SH≦0.25

is preferably satisfied.

This is because, when the above ratio BFH/SH is no more than 0.25, the height of the bead filler, which is made of the high-rigidity member, in the radial direction may be reduced, whereby the vertical spring coefficient of the tire may be effectively reduced and the comfortability may be improved.

Also, when the above ratio BFH/SH is no less than 0.1, the rigidity of the bead portion is ensured and the lateral spring coefficient may be maintained, thereby further ensuring the steering stability.

More specifically, the BFH representing the height of the bead filler in the tire radial direction is preferably 10 mm to 45 mm.

Here, the tire sectional height SH represents a ½ of a difference between an outer diameter of the tire and a diameter of the rim when the tire is mounted on the rim and applied with the internal pressure defined for each vehicle wearing the tire and no load.

FIG. 17 is a cross-sectional view of a tire in the tire width direction according to a second embodiment of the present invention.

FIG. 17 illustrates a half portion of the tire in the tire width direction from the tire equatorial plane CL serving as the boundary.

Note that this tire is in size satisfying the relational expression A or the relational expression B.

As illustrated in FIG. 17, the tire according to the present embodiment includes a belt 3, which is made up of two belt layers 3 a, 3 b by way of example in the figure at a position radially outside the carcass 2 that is composed of a ply of carcass cords radially disposed and toroidally provided around the bead core 1 a embedded in the pair of bead portions 1 of the tire.

The tire according to the present embodiment also includes a sidewall portion 5 connecting to the beat portion 1.

In the illustrated example, the carcass 2 is made up of a carcass main portion 2 a and a folding portion 2 b.

In the illustrated example, further, the bead filler 4 is disposed radially outside the bead core 1 a in the tire radial direction.

FIG. 18(a) is a schematic diagram illustrating a size of a tire member around a sidewall portion of the tire. FIG. 18(b) is a schematic diagram illustrating a size of the tire member around the bead portion of the tire.

Here, according to the present embodiment, as illustrated in FIGS. 17 and 18(a), (b), when Ts represents a gauge of the sidewall portion 5 in the tire maximum width portion and Tb represents a bead width in a tire radial direction center position of the bead core 1 a, a ratio Ts/Tb is 15% to 40%.

Note that the “tire maximum width portion” means a maximum width position in a tire-width-direction cross-section when the tire is mounted on the rim and applied with no load.

The gauge Ts is a sum of thicknesses of all members including rubber, a reinforcing member, the inner liner and the like.

When the tire has a structure in which the bead core is divided into small bead cores by the carcass, Tb represents a distance between a width direction innermost end and an outermost end among all of the small bead cores.

The following is a description of an operation and an effect of the present embodiment.

According to the present embodiment, when the ratio Ts/Tb is within the above range, the rigidity of the tire maximum width portion where great bending deformation occurs during application of a load on the tire is appropriately reduced, thereby reducing the vertical spring coefficient and improving the comfortability.

That is, when the above ratio Ts/Tb exceeds 40%, the gauge of the sidewall portion 5 in the tire maximum width portion is increased, increasing rigidity of the sidewall portion 5 and the vertical spring coefficient. On the other hand, when the above ratio Ts/Tb is smaller than 15%, the lateral spring coefficient becomes too small to ensure the steering stability.

Here, in particular, the gauge Ts of the sidewall portion in the tire maximum width portion is preferably no less than 1.5 mm.

With the gauge Ts of 1.5 mm or more, the rigidity of the tire maximum width portion may be appropriately maintained, preventing reduction in the lateral spring coefficient and further ensuring the steering stability.

On the other hand, in order to further improve the comfortability by effectively reducing the vertical spring coefficient, the gauge Ts of the sidewall portion 5 in the tire maximum width portion is preferably no more than 4 mm.

Also, a diameter Tbc of the bead core 1 a (a maximum width of the bead core in the tire width direction) is preferably 4 mm to 12 mm.

With the Tbc of no less than 4 mm, weight reduction may be achieved while ensuring bending rigidity and torsional rigidity on a rim flange. Also, with the Tbc of no more than 12 mm, the steering stability may be ensured while suppressing weight increase.

FIG. 19 is a cross-sectional view of a tire in the tire width direction according to a third embodiment of the present invention.

FIG. 19 illustrates a half portion of the tire in the tire width direction from the tire equatorial plane CL serving as the boundary.

Note that this tire is in size satisfying the relational expression A or the relational expression B described above.

As illustrated in FIG. 19, the tire according to the present embodiment includes the belt 3, which is made up of two belt layers 3 a, 3 b by way of example in the figure at a position radially outside the carcass 2 that is composed of a ply of carcass cords radially arranged and toroidally provided in a pair of bead portions 1 of the tire.

The tire of the present embodiment also includes the sidewall portion 5 connecting to the bead portion 1.

In the illustrated example, the bead core 1 a is embedded in the bead portion 1, and the bead filler 4 is disposed outside the bead core 1 a in the tire radial direction.

Further, in the illustrated example, the carcass 2 is made up of the carcass main portion 2 a and the folding portion 2 b.

FIG. 20 is a schematic diagram illustrating dimensions of the tire member around the sidewall portion of the tire.

Here, in the tire according to the present embodiment, as illustrated in FIG. 19 and FIG. 20, the ratio Ts/Tc is 5 to 10, the Ts representing the gauge of the sidewall portion 5 in the tire maximum width portion and the Tc representing a diameter of the carcass cord.

Note that the “tire maximum width portion” means the maximum width position in the tire-width-direction cross-section when the tire is mounted on the rim and applied with no load.

The following is a description of an operation and an effect of the present embodiment.

According to the present embodiment, when the ratio Ts/Tc is within the above range, the rigidity of the tire maximum width portion where great bending deformation occurs during application of a load on the tire is appropriately reduced, thereby reducing the vertical spring coefficient and improving the comfortability.

That is, when the ratio Ts/Tc exceeds 10, the gauge of the sidewall portion 4 in the tire maximum width portion is increased, increasing rigidity of the sidewall portion 4 and the vertical spring coefficient. On the other hand, when the ratio Ts/Tc is smaller than 5, the lateral spring coefficient becomes too small to ensure steering stability.

Also, in the tire of the present embodiment, as illustrated in FIG. 19 and FIG. 20, when Ta represents a distance in the tire width direction from a surface of the carcass cord in the tire maximum width portion to a tire outer surface 6, a ratio Ta/Tc is preferably 3 to 6.

With the ratio Ta/Tc of no more than 6, the gauge of the sidewall portion 4 in the tire maximum width portion may be reduced and the rigidity of the sidewall portion 5 may be reduced, thereby reducing the vertical spring coefficient and further improving the comfortability. Also, with the ratio Ta/Tc of no less than 3, the lateral spring coefficient may be ensured, further ensuring the steering stability.

Note that the term “Ta” represents a distance in the tire maximum width portion from the surface of the carcass cord on the width direction outermost side to the tire outer surface.

That is, when the carcass folding portion extends to a radially outer side over the tire maximum width portion, the Ta represents a distance from the surface of the carcass cord in the carcass folding portion to the tire outer surface 6.

Here, the diameter Tc of the carcass cord is preferably 0.4 mm to 0.8 mm. With the diameter Tc of the carcass cord of no more than 0.8 mm, the gauge Ts of the sidewall portion relative to the diameter Tc may be reduced, reducing the vertical spring coefficient. Also, with the diameter Tc of the carcass cord of no less than 0.4 mm, the gauge Ts of the sidewall portion relative to the diameter Tc may be ensured, increasing the lateral spring coefficient and ensuring the steering stability.

EXAMPLES Example 1

In order to confirm the effect of the tire according to the first embodiment, test tires 34-59 and tires according to Comparative Examples 1 to 10 were produced experimentally. Each of the tires includes a carcass, which is composed of a ply of cords radially arranged and toroidally provided between a pair of bead cores, and a bead filler disposed outside the bead core in the tire radial direction.

The following tests were conducted to evaluate performance of the tires.

<Spring Coefficient>

Each of the tires were mounted on the rim and, by using the indoor tester, the deflection amount thereof was measured. The vertical spring coefficient and the lateral spring coefficient were measured from a tangential gradient of a load of 4 kN and are shown as indices relative to those of the tire according to Comparative Example 1 set to 100. The greater the number, the higher the spring constant. Note that the vertical spring coefficient is used as an index of comfortability; the smaller the number, the better the comfortability.

<Rolling Resistance Value (RR Value)>

Each of the above tires was mounted on the rim to obtain a tire-rim assembly, which was then applied with a maximum load defined for each vehicle wearing the tire, for measurement of the rolling resistance thereof under a condition of a drum rotation speed at 100 km/h.

Results of the evaluation are shown as indices relative to the RR value of the tire according to Comparative Example 1 set to 100. The smaller the index, the smaller the rolling resistance.

<Cornering Power>

By using a flat-belt-type cornering test machine, the cornering power was measured with the load at 4 kN and at a speed of 100 km/h.

For evaluation, the cornering power (CP) is shown as an index relative to that of the tire according to Comparative Example 1 set to 100. The greater the index, the preferably higher the cornering power.

<Tire Weight>

The weight of the tires was measured. For evaluation, the weight is shown as an index relative to that of the tire according to Comparative Example 1 set to 100. The smaller the index, the lighter the weight.

Specifications of each of the tires are shown in Table 6, and results of the evaluation are shown in Table 7 and FIGS. 21(a), (b).

TABLE 6 Internal Pressure S1/ SH BFH/ BFH BFW/ Tire Size (kPa) S2 (mm) SH (mm) BDW Comparative 195/65R15 220 4.4 126.8 0.32 41 0.5 Example 1 Comparative 195/65R15 220 4.4 126.8 0.32 41 0.3 Example 2 Comparative 195/65R15 220 2.1 126.8 0.15 19 0.5 Example 3 Comparative 195/65R15 220 1.5 126.8 0.15 19 0.3 Example 4 Test Tire 34 165/65R19 220 4.1 107.3 0.32 34 0.5 Test Tire 35 165/65R19 220 2.9 107.3 0.32 34 0.3 Test Tire 36 165/65R19 220 1.9 107.3 0.15 16 0.5 Test Tire 37 165/65R19 220 1.4 107.3 0.15 16 0.3 Test Tire 38 155/45R21 220 2.7 69.8 0.32 22 0.5 Test Tire 39 155/45R21 220 1.9 69.8 0.32 22 0.3 Test Tire 40 155/45R21 220 1.4 69.8 0.15 10 0.5 Test Tire 41 155/45R21 220 1.1 69.8 0.15 10 0.3 Test Tire 42 165/55R20 220 3.5 90.8 0.32 29 0.5 Test Tire 43 165/55R20 220 2.4 90.8 0.32 29 0.3 Test Tire 44 165/55R20 220 1.6 90.8 0.15 14 0.5 Test Tire 45 165/55R20 220 1.2 90.8 0.15 14 0.3 Test Tire 46 165/65R19 220 1 107.3 0.19 20 0.3 Test Tire 47 165/65R19 220 4 107.3 0.33 35 0.3 Comparative 165/65R19 220 0.9 107.3 0.19 20 0.3 Example 5 Comparative 165/65R19 220 4.1 107.3 0.33 35 0.3 Example 6 Test Tire 48 155/45R21 220 1 69.8 0.32 22 0.3 Test Tire 49 155/45R21 220 4 69.8 0.34 24 0.3 Comparative 155/45R21 220 0.9 69.8 0.32 22 0.3 Example 7 Comparative 155/45R21 220 4.1 69.8 0.34 24 0.3 Example 8 Test Tire 50 165/55R20 220 1 90.8 0.2 18 0.3 Test Tire 51 165/55R20 220 4 90.8 0.33 30 0.3 Comparative 165/55R20 220 0.9 90.8 0.2 18 0.3 Example 9 Comparative 165/55R20 220 4.1 90.8 0.33 30 0.3 Example 10 Test Tire 52 165/65R19 220 2.9 107.3 0.32 34 0.1 Test Tire 53 165/65R19 220 2.9 107.3 0.32 34 0.5 Test Tire 54 165/65R19 220 2.9 107.3 0.32 34 0.09 Test Tire 55 165/65R19 220 2.9 107.3 0.32 34 0.51 Test Tire 56 165/65R19 220 1.5 107.3 0.1 11 0.3 Test Tire 57 165/65R19 220 1.5 107.3 0.25 27 0.3 Test Tire 58 165/65R19 220 1.5 107.3 0.09 10 0.3 Test Tire 59 165/65R19 220 1.5 107.3 0.26 28 0.3

TABLE 7 Lateral Spring Ground- Ground- Vertical Lateral Coefficient/ Contact Contact Spring Spring Vertical Spring RR Length Width Coefficient Coefficient Coefficient Value CP Weight L W OD Comparative 100 100 100 100 100 100 100 100 100 Example 1 Comparative 99 96 97 98 98 98 101 100 100 Example 2 Comparative 96 95 99 95 97 95 101 100 100 Example 3 Comparative 95 93 98 93 96 92 102 100 100 Example 4 Test Tire 34 97 109 112 92 110 93 103 85 109.9 Test Tire 35 96 108 113 89 108 90 104 85 109.9 Test Tire 36 95 107 113 87 105 87 103 85 109.9 Test Tire 37 93 105 113 84 105 84 104 85 109.9 Test Tire 38 97 111 114 74 103 74 103 80 106.1 Test Tire 39 95 110 116 72 103 72 104 80 106.1 Test Tire 40 94 108 115 70 102 69 104 80 106.1 Test Tire 41 92 106 115 69 102 67 105 80 106.1 Test Tire 42 97 112 115 93 113 86 104 86 108.7 Test Tire 43 96 110 115 90 114 83 105 86 108.7 Test Tire 44 95 106 112 87 108 80 104 86 108.7 Test Tire 45 93 104 112 85 108 77 105 86 108.7 Test Tire 46 95 105 111 88 106 89 103 85 109.9 Test Tire 47 99 112 113 94 115 95 103 85 109.9 Comparative 93 98 105 87 99 88 103 85 109.9 Example 5 Comparative 105 115 110 97 116 97 103 85 109.9 Example 6 Test Tire 48 94 107 114 71 103 71 104 80 106.1 Test Tire 49 98 114 116 77 110 77 104 80 106.1 Comparative 92 98 107 70 94 70 104 80 106.1 Example 7 Comparative 104 117 113 80 111 79 104 80 106.1 Example 8 Test Tire 50 95 106 112 89 114 82 105 86 108.7 Test Tire 51 99 114 115 95 118 88 105 86 108.7 Comparative 93 99 106 88 99 81 105 86 108.7 Example 9 Comparative 105 117 111 98 122 90 105 86 108.7 Example 10 Test Tire 52 95 104 109 88 108 89 104 85 109.9 Test Tire 53 98 112 114 94 112 95 104 85 109.9 Test Tire 54 93 97 104 87 106 88 104 85 109.9 Test Tire 55 99 115 116 97 116 97 104 85 109.9 Test Tire 56 93 100 108 84 102 86 104 85 109.9 Test Tire 57 97 110 113 89 105 90 104 85 109.9 Test Tire 58 90 91 101 83 101 85 104 85 109.9 Test Tire 59 99 111 112 92 106 92 104 85 109.9

As illustrated in Tables 6, 7 and FIGS. 21 (a), (b), each of the test tires satisfying the relational expression A or the relational expression B and, simultaneously, having S1/S2 within a favorable range is lightweight and has less rolling resistance as well as a small vertical spring coefficient, thus providing excellent comfortability.

Also, the test tires having the ratio BFW/BDW within the favorable range have smaller vertical spring coefficients while ensuring the cornering power.

Further, the test tires having a favorable ratio BFH/SH may reduce the vertical spring coefficient while ensuring the cornering power.

Next, in order to see the effect of high internal pressure of the tire, tests for evaluation of performance of test tires 60 to 71 and tires according to Comparative Examples 11 to 13 with high internal pressure shown below were conducted.

Specifications of each of the tires are shown in Table 8, and results of the evaluation are shown in Table 9 and FIGS. 22(a), (b).

TABLE 8 Internal Pressure S1/ SH BFH/ BFH BFW/ Tire Size (kPa) S2 (mm) SH (mm) BDW Comparative 195/65R15 220 4.4 126.8 0.32 41 0.5 Example 11 Comparative 195/65R15 240 4.4 126.8 0.32 41 0.5 Example 12 Comparative 195/65R15 250 4.4 126.8 0.32 41 0.3 Example 13 Test Tire 60 165/65R19 240 2.9 107.3 0.32 34 0.3 Test Tire 61 165/65R19 250 2.9 107.3 0.32 34 0.3 Test Tire 62 165/65R19 240 1.4 107.3 0.15 16 0.3 Test Tire 63 165/65R19 250 1.4 107.3 0.15 16 0.3 Test Tire 64 155/45R21 240 1.9 69.8 0.32 22 0.3 Test Tire 65 155/45R21 250 1.9 69.8 0.32 22 0.3 Test Tire 66 155/45R21 240 1.1 69.8 0.15 10 0.3 Test Tire 67 155/45R21 250 1.1 69.8 0.15 10 0.3 Test Tire 68 165/55R20 240 2.4 90.8 0.32 29 0.3 Test Tire 69 165/55R20 250 2.4 90.8 0.32 29 0.3 Test Tire 70 165/55R20 240 1.2 90.8 0.15 14 0.3 Test Tire 71 165/55R20 250 1.2 90.8 0.15 14 0.3

TABLE 9 Lateral Spring Ground- Ground- Vertical Lateral Coefficient/ Contact Contact Spring Spring Vertical Spring RR Length Width Coefficient Coefficient Coefficient Value CP Weight L W OD Comparative 100 100 100 100 100 100 100 100 100 Example 11 Comparative 104 103 99 99 98 100 96 100 100 Example 12 Comparative 106 105 99 96 94 100 93 100 100 Example 13 Test Tire 60 97 110 113 88 105 90 102 85 109.9 Test Tire 61 98 114 116 85 107 90 101 85 109.9 Test Tire 62 94 107 114 82 103 84 103 85 109.9 Test Tire 63 95 111 117 79 105 84 102 85 109.9 Test Tire 64 97 112 115 71 102 72 103 80 106.1 Test Tire 65 98 116 118 68 104 72 102 80 106.1 Test Tire 66 94 108 115 68 101 67 103 80 106.1 Test Tire 67 95 111 117 65 103 67 102 80 106.1 Test Tire 68 97 113 116 89 110 83 103 86 108.7 Test Tire 69 98 117 119 86 112 83 102 86 108.7 Test Tire 70 95 106 112 84 106 77 103 86 108.7 Test Tire 71 96 109 114 81 109 77 102 86 108.7

Comparisons between Tables 9 and 7 and between FIGS. 21 (a), (b) and FIGS. 22(a), (b) show that use of the tire with high internal pressure further reduces the tire rolling resistance and further improves the cornering power.

Example 2

Next, in order to confirm the effect of the tire according to the second embodiment, test tires 72 to 82 and tires according to Comparative Examples 14 to 23 were produced experimentally. Each of the tires includes the carcass, which is composed of a ply of cords radially arranged and toroidally provided between a pair of bead cores, and a pair of sidewall portions connected to the bead portions.

In order to evaluate the performance of these tires, in a manner similar to Example 1, tests were conducted for evaluation of the spring coefficients, the rolling resistance value (RR value), the cornering power, and the tire weight.

Note that, for evaluation, the spring coefficients are shown as indices relative to that of the tire according to Comparative Example 14 set to 100. The greater the value, the higher the spring constant. Also, the rolling resistance value (RR value), for evaluation thereof, is shown as an index relative to that of the tire according to Comparative Example 14 set to 100. The smaller the index, the smaller the rolling resistance. Further, the cornering power, for evaluation thereof, is shown as an index relative to that of the tire according to Comparative Example 14 set to 100. The greater the index, the preferably higher the cornering power. Also, the tire weight, for evaluation thereof, is shown as an index relative to that of the tire according to Comparative Example 14 set to 100. The smaller the value, the lighter the weight.

Specifications of each of the tires are shown in Table 10, and results of the evaluation are shown in Table 11 and FIGS. 23(a), (b).

Note that in Table 10 the term “SH” means a sectional height (a cross-sectional height of the tire).

TABLE 10 Internal Ratio Pressure SH Ts/Tb Ts Tb Tbc Tire Size SW/OD (kPa) (mm) (%) (mm) (mm) (mm) Comparative 195/65R15 0.31 220 126.8 67 10 15 10 Example 14 Comparative 195/65R15 0.31 220 126.8 33 5 15 10 Example 15 Comparative 165/65R19 0.24 220 107.3 71 10 14 8 Example 16 Test Tire 72 165/65R19 0.24 220 107.3 29 4 14 8 Comparative 165/55R21 0.23 220 107.3 69 9 13 6 Example 17 Test Tire 73 165/55R21 0.23 220 107.3 27 3.5 13 6 Comparative 155/55R21 0.22 220 85.3 71 10 14 4 Example 18 Test Tire 74 155/55R21 0.22 220 85.3 29 4 14 4 Comparative 155/55R21 0.22 220 85.3 9 1.3 14 4 Example 19 Test Tire 75 155/55R21 0.22 220 85.3 29 4 14 3 Test Tire 76 165/65R19 0.24 220 107.3 15 2.3 15 8 Test Tire 77 165/65R19 0.24 220 107.3 40 5.2 13 8 Comparative 165/65R19 0.24 220 107.3 14 1.7 12 8 Example 20 Comparative 165/65R19 0.24 220 107.3 41 6.2 15 8 Example 21 Test Tire 78 155/55R21 0.22 220 85.3 15 2.3 15 4 Test Tire 79 155/55R21 0.22 220 85.3 40 5.2 13 4 Comparative 155/55R21 0.22 220 85.3 14 1.7 12 4 Example 22 Comparative 155/55R21 0.22 220 85.3 41 6.2 15 4 Example 23 Test Tire 80 155/55R21 0.22 220 85.3 15 1.5 10 4 Test Tire 81 155/55R21 0.22 220 85.3 29 4 14 13 Test Tire 82 155/55R21 0.22 220 85.3 17.5 1.4 8 4

TABLE 11 Lateral Ground- Ground- Spring/ Contact Contact Vertical Lateral Vertical RR Length Width Spring Spring Spring Value CP Weight L W OD Comparative 100 100 100 100 100 100 100 100 100 Example 14 Comparative 99 97 98 97 98 97 101 100 100 Example 15 Comparative 115 111 96 97 104 93 102 85 109.9 Example 16 Test Tire 72 97 107 110 96 102 90 103 85 109.9 Comparative 130 116 89 85 104 86 103 80 112.7 Example 17 Test Tire 73 97 111 114 84 101 83 104 80 112.7 Comparative 120 111 92 98 109 77 104 86 110.9 Example 18 Test Tire 74 97 104 106 96 105 75 105 86 110.9 Comparative 96 97 101 80 95 72 106 86 110.9 Example 19 Test Tire 75 95 96 101 78 102 74 106 86 110.9 Test Tire 76 97 102 105 94 100 88 103 85 109.9 Test Tire 77 99 109 110 95 106 93 103 85 109.9 Comparative 98 97 99 94 98 86 103 85 109.9 Example 20 Comparative 110 109 99 97 110 98 103 85 109.9 Example 21 Test Tire 78 98 100 102 95 103 73 105 86 110.9 Test Tire 79 99 107 106 97 108 77 105 86 110.9 Comparative 98 97 99 94 98 72 105 86 110.9 Example 22 Comparative 109 106 97 99 110 80 105 86 110.9 Example 23 Test Tire 80 97 97 100 81 102 70 106 86 110.9 Test Tire 81 99 103 104 83 104 73 106 86 110.9 Test Tire 82 95 95 100 80 101 69 106 86 110.9

As shown in Tables 10, 11 and FIGS. 23 (a), (b), each of the test tires satisfying the relational expression A or the relational expression B and, simultaneously, having the ratio Ts/Tb within the favorable range is lightweight and has less rolling resistance as well as smaller vertical spring coefficient, thus providing excellent comfortability.

Also, the test tires having a favorable gauge Ts have excellent cornering power.

Further, the test tires having favorable values of the diameter Tbc of the bead core also have excellent cornering power.

Next, in order to see the effect of the tire with high internal pressure, tests for evaluation of performance of test tires 83 to 88 and tires according to Comparative Examples 24 and 25 with high internal pressure shown below were conducted.

Specifications of each of the tires are shown in Table 12, and results of the evaluation are shown in Table 13 and FIGS. 24(a), (b).

TABLE 12 Internal Ratio Pressure SH Ts/Tb Ts Tb Tbc Tire Size SW/OD (kPa) (mm) (%) (mm) (mm) (mm) Comparative 195/65R15 0.31 220 126.8 67 10 15 10 Example 14 Comparative 195/65R15 0.31 240 126.8 67 10 15 10 Example 24 Comparative 195/65R15 0.31 250 126.8 67 10 15 10 Example 25 Test Tire 83 165/65R19 0.24 240 107.3 29 4 14 8 Test Tire 84 165/65R19 0.24 250 107.3 29 4 14 8 Test Tire 85 165/55R21 0.23 240 107.3 27 3.5 13 6 Test Tire 86 165/55R21 0.23 250 107.3 27 3.5 13 6 Test Tire 87 155/55R21 0.22 240 85.3 29 4 14 4 Test Tire 88 155/55R21 0.22 250 85.3 29 4 14 4

TABLE 13 Lateral Ground- Ground- Spring/ Contact Contact Vertical Lateral Vertical RR Length Width Spring Spring Spring Value CP Weight L W OD Comparative 100 100 100 100 100 100 100 100 100 Example 14 Comparative 110 106 94 99 98 100 96 100 100 Example 24 Comparative 115 110 87 96 96 100 93 100 100 Example 25 Test Tire 83 98 109 111 95 103 90 102 85 109.9 Test Tire 84 99 118 119 90 108 90 100 85 109.9 Test Tire 85 98 112 114 83 104 83 103 80 112.7 Test Tire 86 99 119 120 77 110 83 101 80 112.7 Test Tire 87 98 105 107 95 106 75 104 86 110.9 Test Tire 88 99 111 112 90 111 75 100 86 110.9

From Table 13 and FIGS. 24(a), (b), it can be seen that using the tire with high internal pressure may reduce the tire rolling resistance value and improve the cornering power.

Example 3

Next, in order to see the effect of a tire according to Example 3, test tires 89 to 103 and tires according to Comparative Examples 26 to 34 were produced experimentally. Each of the tires includes the carcass, which is composed of a ply of cords radially arranged and toroidally provided between a pair of bead portions, and a pair of sidewall portions connected to the bead portions.

In order to evaluate the performance of these tires, in a manner similar to Example 1, tests were conducted for evaluation of the spring coefficients, the rolling resistance value (RR value), the cornering power, and the tire weight.

Note that, for evaluation, the spring coefficients are shown as indices relative to those of the tire according to Comparative Example 26 set to 100. The greater the value, the higher the spring constant. Also, the rolling resistance value (RR value), for evaluation thereof, is shown as an index relative to that of the tire according to Comparative Example 26 set to 100. The smaller the index, the smaller the rolling resistance. Further, the cornering power, for evaluation thereof, is shown as an index relative to that of the tire according to Comparative Example 26 set to 100. The greater the index, the preferably higher the cornering power. Also, the tire weight, for evaluation thereof, is shown as an index relative to that of the tire according to Comparative Example 26 set to 100. The smaller the value, the lighter the weight.

Specifications of each of the tires are shown in Table 14, and results of the evaluation are shown in Table 15 and FIGS. 25(a), (b).

TABLE 14 Internal Ratio Pressure Ts Ta Tc Tire Size SW/OD (kPa) (mm) (mm) (mm) Ts/Tc Ta/Tc Comparative 195/65R15 0.31 220 10 6 0.66 15.2 9.1 Example 26 Comparative 195/65R15 0.31 220 5 3 0.66 7.6 4.5 Example 27 Comparative 165/65R19 0.24 220 10 5 0.5 20 10 Example 28 Test Tire 89 165/65R19 0.24 220 4 2.5 0.5 8 5 Comparative 165/55R21 0.23 220 9 5.5 0.5 18 11 Example 29 Test Tire 90 165/55R21 0.23 220 3.5 2.8 0.5 7 5.6 Comparative 155/55R21 0.22 220 10 6 0.55 18.2 10.9 Example 30 Test Tire 91 155/55R21 0.22 220 4 2 0.55 7.3 3.6 Comparative 155/55R21 0.22 220 10 6 0.8 12.5 7.5 Example 31 Test Tire 92 165/65R19 0.24 220 2.5 2.5 0.5 5 5 Test Tire 93 165/65R19 0.24 220 5 2.5 0.5 10 5 Comparative 165/65R19 0.24 220 2.3 2.5 0.5 4.5 5 Example 32 Comparative 165/65R19 0.24 220 6.3 2.5 0.5 12.5 5 Example 33 Test Tire 94 155/55R21 0.22 220 2.8 2 0.55 5 3.6 Test Tire 95 155/55R21 0.22 220 5.5 2 0.55 10 3.6 Comparative 155/55R21 0.22 220 2.5 2 0.55 4.5 3.6 Example 34 Test Tire 96 155/55R21 0.22 220 4 1.7 0.55 7.3 3 Test Tire 97 155/55R21 0.22 220 4 3.3 0.55 7.3 6 Test Tire 98 155/55R21 0.22 220 4 1.4 0.55 7.3 2.5 Test Tire 99 155/55R21 0.22 220 4 3.9 0.55 7.3 7 Test Tire 100 155/55R21 0.22 220 5.1 2.5 0.7 7.3 3.6 Test Tire 101 155/55R21 0.22 220 2.9 1.4 0.4 7.3 3.6 Test Tire 102 155/55R21 0.22 220 5.8 2.9 0.8 7.3 3.6 Test Tire 103 155/55R21 0.22 220 2.6 1.3 0.35 7.3 3.6

TABLE 15 Lateral Ground- Ground- Spring/ Contact Contact Vertical Lateral Vertical RR Length Width Spring Spring Spring Value CP Weight L W OD Comparative 100 100 100 100 100 100 100 100 100 Example 26 Comparative 104 84 81 97 86 97 101 100 100 Example 27 Comparative 110 112 101 92 110 93 105 85 109.9 Example 28 Test Tire 89 97 106 107 87 106 90 106 85 109.9 Comparative 120 126 104 74 113 74 103 80 112.7 Example 29 Test Tire 90 99 116 111 73 105 72 103 80 112.7 Comparative 113 114 101 93 110 86 103 86 110.9 Example 30 Test Tire 91 98 110 110 91 107 83 103 86 110.9 Comparative 130 120 92 106 110 93 101 86 110.9 Example 31 Test Tire 92 95 101 106 85 103 88 106 85 109.9 Test Tire 93 99 107 108 89 109 93 106 85 109.9 Comparative 95 94 99 83 97 85 106 85 109.9 Example 32 Comparative 110 108 98 88 111 97 106 85 109.9 Example 33 Test Tire 94 97 103 106 88 104 80 103 86 110.9 Test Tire 95 99 112 113 93 110 86 103 86 110.9 Comparative 96 95 99 92 98 79 103 86 110.9 Example 34 Test Tire 96 98 102 104 88 103 80 103 86 110.9 Test Tire 97 98 109 111 94 107 85 103 86 110.9 Test Tire 98 97 96 99 85 101 78 103 86 110.9 Test Tire 99 99 111 112 97 110 89 103 86 110.9 Test Tire 100 99 113 114 93 112 85 103 86 110.9 Test Tire 101 96 104 108 88 104 81 103 86 110.9 Test Tire 102 99 114 115 95 115 87 103 86 110.9 Test Tire 103 95 98 103 85 102 79 103 86 110.9

[Table 15-2]

As shown in Tables 14, 15 and FIGS. 25(a), (b), each of the test tires satisfying the relational expression A or the relational expression B and, simultaneously, having the ratio Ts/Tc within a favorable range is lightweight and has less rolling resistance as well as small vertical spring coefficient, thus providing excellent comfortability.

Also, the test tires having Ta/Tc in a favorable range have smaller vertical spring coefficients while maintaining approximately the same cornering power.

Further, the test tires having favorable values of the cord diameter Tc have further smaller vertical spring coefficients and improved cornering power.

Next, in order to see the effect of the tire having high internal pressure, tests for evaluation of performance of test tires 104 to 109 and tires according to Comparative Examples 35 to 37 with high internal pressure shown below were conducted.

Specifications of each of the tires are shown in Table 16, and results of the evaluation are shown in Table 17 and FIGS. 26(a), (b).

TABLE 16 Internal Ratio Pressure Ts Ta Tc Tire Size SW/OD (kPa) (mm) (mm) (mm) Ts/Tc Ta/Tc Comparative 195/65R15 0.31 220 10 6 0.66 15.2 9.1 Example 35 Comparative 195/65R15 0.31 240 10 6 0.66 15.2 9.1 Example 36 Comparative 195/65R15 0.31 250 10 6 0.66 15.2 9.1 Example 37 Test Tire 104 165/65R19 0.24 240 4 2.5 0.5 8 5 Test Tire 105 165/65R19 0.24 250 4 2.5 0.5 8 5 Test Tire 106 165/55R21 0.23 240 3.5 2.8 0.5 7 5.6 Test Tire 107 165/55R21 0.23 250 3.5 2.8 0.5 7 5.6 Test Tire 108 155/55R21 0.22 240 4 2 0.55 7.3 3.6 Test Tire 109 155/55R21 0.22 250 4 2 0.55 7.3 3.6

TABLE 17 Lateral Ground- Ground- Spring/ Contact Contact Vertical Lateral Vertical RR Length Width Spring Spring Spring Value CP Weight L W OD Comparative 100 100 100 100 100 100 100 100 100 Example 35 Comparative 110 106 94 99 98 100 97 100 100 Example 36 Comparative 115 110 87 96 96 100 93 100 100 Example 37 Test Tire 104 98 109 111 95 103 90 102 85 109.9 Test Tire 105 99 119 120 89 109 90 100 85 109.9 Test Tire 106 98 111 113 84 103 84 103 80 112.7 Test Tire 107 99 117 118 79 108 84 101 80 112.7 Test Tire 108 98 106 108 94 107 74 104 86 110.9 Test Tire 109 99 110 111 91 110 74 100 86 110.9

From Table 17 and FIGS. 26 (a), (b), it can be seen that, when the tire having high internal pressure is used, the tire rolling resistance value is further reduced and cornering power is further improved.

REFERENCE SIGNS LIST

-   1 bead portion -   1 a bead core -   2 carcass -   2 a carcass main body -   2 b carcass folding portion -   3 belt -   4 bead filler -   5 side wall portion -   6 tire outer surface 

1. A passenger vehicle pneumatic radial tire including a carcass, which is composed of a ply of carcass cords radially arranged and toroidally provided between a pair of bead portions, and a pair of sidewall portions connected to the bead portions, wherein when the tire is mounted on a rim and applied with internal pressure of at least 250 kPa, with a tire cross-sectional width SW of smaller than 165 (mm), a ratio of the tire cross-sectional width SW to a tire outer diameter OD, SW/OD, is no more than 0.26, with the tire cross-sectional width SW of 165 (mm) or larger, the tire cross-sectional width SW and the tire outer diameter OD satisfy a relational expression: OD≧2.135×SW+282.3, and a ratio Ts/Tc is 5 to 10, the Ts representing a gauge of the sidewall portion in a tire maximum width portion and Tc representing a diameter of the carcass cord.
 2. A passenger vehicle pneumatic radial tire including a carcass, which is composed of a ply of carcass cords radially arranged and toroidally provided between a pair of bead portions, and a pair of sidewall portions connected to the bead portions, wherein when the tire is mounted on a rim and applied with internal pressure of at least 250 kPa, a tire cross-sectional width SW and a tire outer diameter OD satisfy a relational expression: OD≧−0.0187×SW²+9.15×SW−380, and a ratio Ts/Tc is 5 to 10, the Ts representing a gauge of the sidewall portion in a tire maximum width portion and Tc representing a diameter of the carcass cord.
 3. The passenger vehicle pneumatic radial tire according to claim 1, wherein, when Ta represents a distance in a tire width direction from a surface of the carcass cord to a tire outer surface, a ratio Ta/Tc is 3 to
 6. 4. The passenger vehicle pneumatic radial tire according to claim 1, wherein the diameter Tc of the carcass cord is 0.4 mm to 0.8 mm. 